The deposition of solids onto the structural surfaces in contact with water is a serious problem in numerous industrial operations. The buildup of solids is especially problematic and undesirable in systems where heat transfer is conducted across these surfaces. The heat exchange surfaces in cooling water systems and steam condensate systems are particularly adversely affected by the deposition of solids because the greater the amount of deposited solids, the lower the efficiency in conducting heat across those surfaces. A unique type of deposit is the scale caused by silica (based on silicon dioxide) and precipitated silicates (based on the salts of water soluble silica). Silica and silicate scale have exceedingly low thermal conductivity and, as a result, may reduce the heat transfer coefficient of a heat exchanger by as much as 90 percent.
Silica and silicate scale deposition is considered a unique problem because treatment programs effective against the deposition of more common scale forming species, such as calcium or magnesium containing carbonates, phosphonates and phosphates, are not effective in preventing silica and silicate scale deposition. This distinction may be based, in part, on the amorphous character of the silica and silicate species in contrast to the crystalline character of carbonates, phosphonates and phosphates.
Conventional treatment programs for dealing with the more common scale species involve maintaining the ions in solution. This technique cannot be applied to silica and silicate scale deposits since there are no known silica solubilizing chemicals. These deposits are generally prevented or minimized by keeping the concentration of silica and/or the silicates below their solubility limits. Such an approach requires the treatment of the feedwater prior to addition to the cooling or steam generating system. Such treatments include coagulation or filtration and are only marginally effective. Even with such precautions, frequent blowdown of the recirculating system may be required in order to maintain the lowest possible concentrations of these species.
It is an object of the present invention to provide a treatment composition that will be highly effective in reducing the deposition of silica and/or silicate precipitates on the internal structural surfaces of heat exchangers in various steam generating and cooling water systems.